1. Field of the Invention
The present invention relates to inflatable fabric airbag applications for limiting the escape of inflation gas around the inflator. More specifically, the present invention relates to airbag designs that can achieve and maintain high internal pressures while having a partially exposed inflator.
2. Description of Related Art
Inflatable safety restraint devices, or airbags, are well accepted for use in motor vehicles and have been credited with preventing numerous deaths and injuries. Inflatable airbags are now mandatory on most new vehicles. Airbags are typically installed as part of a system with an airbag module in the steering wheel on the driver's side of a car and in the dashboard on the passenger side of a car. In the event of an accident, a sensor within the vehicle measures abnormal deceleration and triggers the ignition of a charge contained within an inflator. Expanding gases from the charge travel through conduits and fill the airbags, which immediately inflate in front of the driver and passenger to protect them from harmful impact with the interior of the car.
During a front end collision, there is a tendency for an occupant, particularly one who is not properly restrained by a seat belt, to slide forward along the seat and “submarine” under the airbag (hereinafter referred to as the “primary airbag”). When the occupant submarines, the primary airbag is less effective in protecting the occupant. Such submarining causes the vehicle occupant's knees to contact the instrument panel or structure beneath the panel. Further injuries can occur when the occupant's legs move forward such that the knees are trapped in or beneath the instrument panel just before the foot well collapses. As the foot well collapses, the vehicle occupant's feet are pushed backward, which causes the knees to elevate and become further trapped. As the foot well continues to crush, the load on the trapped legs increase and can cause foot, ankle, and tibia injuries.
In order to prevent such injuries, inflatable knee airbag systems have been developed to engage an occupant's knees or lower legs and prevent submarining under the primary airbag. Knee airbag systems are generally positioned in the lower portion of the instrument panel. The use of fabric airbags in knee airbag applications presents particular problems. An occupant's legs have a very small contact area, and therefore exhibit a high force over a small area when in contact with the cushion. The lower legs tend to “knife” through the fabric airbag if there is not sufficient internal pressure to withstand such force. In order to prevent knifing through the airbag chamber, fabric knee airbags need to be inflated to two to three times the pressure normally applied in conventional fabric airbag systems.
Furthermore, in an effort to further improve driver and passenger safety, side-impact airbags have been developed. These airbags function by providing a buffer between the side of a vehicle and the body of a driver or passenger of the vehicle during accidents in which the side of the vehicle is struck by another vehicle or other object. This class of airbags was typically designed to deploy from a compartment within the occupant's seat. The seat mounted airbag may inflate beside an occupant to protect the pelvis and thorax of the occupant against lateral impact.
However, side airbags need to maintain higher cushion pressures during the initial stages of deployment to enable the airbag to break out of the plastic airbag housing module and the seam of the seat. Consistent seat breakout has been a problem at low temperatures, e.g., −40 degrees Celsius, and with inflators that perform at the lower end of the Bell curve with respect to the amount of inflation gas generated compared to other inflators. Insufficient internal pressure is usually the reason for failed seat breakout at low temperatures and for lower limit inflator performance. Furthermore, if the internal pressure of the side airbag is inadequate, the likelihood of a vehicle occupant striking the wall of the vehicle despite the existence of the airbag is increased. Such an event is called a “strikethrough” and may be attributed to insufficient internal pressure.
One reason side and knee airbags are unable to achieve and maintain high internal pressures is that inflation gases are able to escape the cushion through the cushion opening that receives the inflator. One method previously employed to try and limit exiting inflation gases is to fold a fabric flap or flaps over the opening through which the inflator was inserted. This method, however, is not able to consistently maintain the high pressures needed for knee and side airbag applications because gaps still exist between the inflator and the airbag fabric.
Another previously employed method to restrict the exiting of inflation gases adjacent the inflator is to completely enclose the inflator within the cushion. However, it is difficult to assemble the inflator into the cushion in high pressure airbag designs. First, the wire harness connected to the inflator exiting the cushion can be pinched easily between the inflator housing and the airbag module housing. Second, a completely internal inflator requires additional electrical check to ensure that the electrical characteristics are still functioning properly. Third, push/pull testing is required in which a universal connector snaps into the inflator and 10 pounds of force is applied to each line to ensure proper connection to the inflator. Consequently, a fully enclosed inflator requires additional time consuming and costly procedures to ensure the inflator will function properly.
Accordingly, a need exists for an inflatable fabric cushion that can receive an inflator, but provide for an exposed inflator squib exterior to the cushion. A need also exists for an inflatable fabric cushion that can be sealed about its openings adjacent a partially enclosed inflator to limit the escape of inflation gas. Furthermore, a need exists for a fabric knee or side airbag that can maintain high internal pressures in order to prevent occupant strikethrough or knifing through the inflated cushion, and effective seat breakout in side airbag applications. Such a device is disclosed and claimed herein.